The FBI is on a manhunt for a suspected killer who could be hiding in the Central Valley's backyard. A $100,000 reward is out for a man the FBI says bludgeoned his entire family -- then burned their bodies 38 years ago.

The FBI released a bust, on what William Bradford Bishop Junior may look like today. The bust, molded by a world renowned artist, is an age progression based on an image of Bishop taken in the 1970's.

Agents say in 1976, Bishop used a sledgehammer to kill his mother, wife and their three young sons.

Due to the grisly deaths, the FBI dubbed Bishop the nickname "Family Annihilator."

"Bishop drove to North Carolina and tried to bury his wife, his mother and his three sons in a shallow grave," said Ron Hosko, assistant director of the FBI's Criminal Investigative Division. "He attempted to cover that up by setting fire to the grave."

The killings happened in Bethesda, Maryland. Agents say the family murders rocked the community -- and still haunt the agents on the case today.

Hosko added, "To be able to take a hammer to your children's heads and faces while they're sleeping really shows the brutality of the crime."

Aside from a few sightings in the days after the extraordinarily brutal murders -- Bishop has not been seen.

Agents say he has family in California and a huge affinity for the Sierra Nevada Mountains.

The FBI says because he's an avid outdoorsman there is good reason to believe Bishop could be hiding anywhere from Lake Tahoe -- to Yosemite -- or further south as he considered California home.

Montgomery County Police Chief Tom Manger said, "News spreads fast, and all we need is just one person to call us with the right tip, and we can find Bradford Bishop."

A task force of local and federal agents re-launched this cold case last year. And just added Bishop to the FBI top 10 fugitive list.

They're releasing mounds of files, pictures and other information in hopes someone will spot the now 77-year-old William Bradford Bishop Junior.